Fluid pressure braking system



May 6, 1941. H. c. BOWEN 2,241,112

FLUID PRESSURE BRAKING SYSTEM Filed March 24, 1958 l 62 26 54 20 52INVENTOR.

' #feels-@TC 50mi-N 72 g Z. vmw, @tmf/44u44 ATTORNEYS.

Patented May I 6, 1941 UNiTED STATES Aini'rlsNT fori-ICE .Herbert C.Bowen, Detroit, Mich., assignmto HydraulicBrake Company, Detroit,Mich.,A a corporation of California Application March 24A, 1938, SerialNo. 197,796

(Cl. (S-54.6)

Claims.

This invention relates to fluid pressure braking systems.

Broadly the invention comprehends a fiuid` pressure braking system for amotor vehicle including a fluid pressure producing device operative tomaintain a predetermined pressure on the fluid in the cylinder so thatlost `motion on the initialv operation vof the system may be avoided.

An object of the invention is to provide a fluid pressure producingdevice having means for maintaining a predetermined pressure on thefluid in the compression chamber, and means compensating for expansionand contraction of the fluid due to temperature changes.

Another object of the invention is to provide a fluid pressure producingdevice in which the conventional compensating port providing acommunication between the compression chamber and the reservoir of thedevice is eliminated. Another object ofthe invention is to provide afluid pressure producing device, including a cylinder and a pistonmovable in the cylinder for producing pressure, having embodied thereinmeans for maintaining a predetermined pressure on the fluid in thecylinder and means compensating for expansion and contraction of theiluid due to temperature changes.

Other objects and advantages of the invention will appear from thefollowing description taken y in connection with the drawing forming apart as bya plug i8 having openings I8 for venting -the reservoir to theatmosphere. A cylinder 20 formed at the base of the reservoir has' oneend open land the other end closed as by a head 22 provided with adischarge port 24 controlled by a two-way valve 28, and arranged in thewall of the cylinder is a port 28 providing a communication between thecylinder and the reservoir.

A fluid pressure delivery /pipe or conduit 30 suitably connected to thedischarge port 24 of the cylinder has branches connected respectively tofluid pressure actuated motors 32, preferably arranged in pairs,onepair, for actuating brakes associated with thev front wheels of avehicle and another pair for actuating brakes associated with the rearwheels of the vehicle.

The brakes may be of any conventional type. As shown, each of the brakesincludes a flxd supportl or backing plate 34, adapted to be secured toan axle or to an axle housing, a rotatable drum 36 associated with thebacking plate adapted toV be secured to a wheel, a pair of correspondinginterchangeable friction elements or shoes V38 pivoted on the backingplate for cooperation with the drum, a retractile spring 40 connectingthe shoes, and a motor corresponding to the motors 32 connected to theshoes and operative to actuat the shoes into engagement with the drumagainst the resistance of th retractile spring. i

`A piston 42 reciprocable in the cylinder 28 is held againstdisplacement by a washer 44 seated on an annular shoulder in the openend of the cylinder, and secured in place as by a retaining ring 46seated in a groove in the wall of the cylinder. The piston 42 includes ahead 43, a reduced .body portion 50 providing in conjunction with thewall of the cylinder 20 an annular chamber 52 communicating with thereservoir I2 by way of the port 28, and a skirt 54 having seated thereona sealing cup 56 for inhibiting seepage of fluid from the cylinder pastthe piston. The head 48 of the piston has spaced passages 58therethrough providing communications between the annular chamber 52 andthat portion of the cylinder forward of the piston. A sealing cup 68seated on the head of the piston controls the passages 58, and a spring62 interposed between the sealing cup and the two-w-ay valve 26 retainsthe cup and valve against displacement and also serves to return thepiston to its retracted position.

The piston is bored to provide a chamber 64 having a port 66 located inthe head of thepiston providing a communication between the chamber 84and that portion of the cylinder 20 forward of the piston, and arrangedin the wall of the chamber 64 are ports 68 and 10 providingcommunications between the chamber 64 and the annular chamber 52. 4

A plunger 12 reciprocable in the chamber 64 is retained againstdisplacement by.a washer 14 seated on an annular shoulder in the openend Vof the chamber and secured in place by a retaining ring 16 seatedin a groove in the wall of the chamber. The plunger 12 has a concentricextension 18,ad-apted to enter and close the port 88, and a recess inthe back thereof for the reception of the operatingmeans. Movement ofthe plunger 12 in the chamber 64 is limited by suitable cooperativestops ,indicated at 82.

When the plunger is advanced to close the port 88 in the head of thepiston, the end of the extension enters the port 88 and abuts thesealing cup 80 so as to effectively seal the port. The extension 'I8 hassleeved thereon and seated on the head of the plunger a sealing cup 84for back ofthe plunger 12 has thereon a coupling 08 connected as by aflexible boot 80 to the open end of the cylinder 20 for the exclusion ofdust and other foreign substances from the cylinder. A

' rod |00 connects the coupling to a foot pedal lever |02 pivotallysupported on a bracket |04 and connected by a retractile spring |08 to afixed support |08.

In a normal operation, upon depressing the lfoot pedal lever |02, forceis transmitted therefrom through the vrod and thrust pin 84 to the`plunger 12, resulting in advancing the plunger to its maximum allowabledetermined by the stops 82.. During this movement of the plunger,v

the extension 18 enters and closes the port 88 in the head 48 of thepiston 42 and abuts the sealing cup 80 to effectively seal the port.Thereafter the plunger and piston move as a single unit, and the fluidin the cylinder 20 forward of the piston is displaced therefrom, pastthe two-way valve 28, through the discharge port 24 and fluid deliverypipe 30 and the branches thereof into the fluid pressure actuated motors32, causing energization of the motors, resulting in4 actuation of theshoes 38 of the respective brake structures into engagement with thedrums. i

` Atvthe conclusion of a braking operation, th-e 'foot pedal lever |02is released and is returned to its retracted position under theinfluence of the retractile spring |08. This movement of the foot pedallever retracts the rod |00 and thrust pin 94, resulting in release ofthe plunger 12 and consequent release of the piston 42, whereupon thereis relative movement between the plunger and the piston due to theinfluence of the spring 92 urging the plungerv to its retractedposition` pletely fill the cylinder. nder thiscondition, the pressure onthe fluid in the cylinder is received on the head of the piston 88slidable. on

f the extension of the. plunger in the chamber 84,

resulting inmovement of the piston 48 against the resistance of thespring 88, so as to uncover the port 'I0 to permit excess fluid toescape from that portion of the cylinder forward of the piston throughthe p ort 88 in the head of the piston into the chamber 84, thencethrough the port l0 into the annular chamber. and from there through theport 28 into the reservoir. The piston 88 is then urged by the spring 8lto cover the port 10 and to impose a predetermined pressure on theiluidin the cylinder forward of the piston 42 so that in a subsequentoperation all lost motion, such as advancing the piston to cover thecompensating port, as in conventional' devices of this character, may beavoided.

If the braking systemis exposed to a decrease in temperature, the fluidln the lines and wheel cylinders contractsvand such contraction iscompensated for under normal conditions by piston and concomitantly withthis relative movement of the piston and the plunger, the piston isreturned to its retracted position under thev influence of the spring82.

As the piston 42 returns to its retracted position, a partial vacuum iscreated in that portion of the cylinder forward of the piston, resultingin drawing fluid from the reservoir through the port 28 into the annularvchamber V52, thence through the passages 58 in the head 48 of thepiston, past the sealing cup 60, into that portion of the cylinderforward of the piston, completely filling the cylinder, and during thisperiod fluid is returning from the fluid pressure actuated motors 32 andthefluid pressure delivery pipe 30 and the branches thereof to thecylinder,`under the influence of the retractile springs 40 connecttityof fluid in excess oi' that required to com- 88 which advances towardthe right as viewed in Figure 2 under the influence oi' the spring 88 todisplace sufllcient fluid from the chamber 84 through port 88 tocompensate for such contraction. On the other hand, where the brakingsystem is subjected to rise in temperature, the fluid in the lines andwheel cylinders expands and forces piston 88 toward the lei't to uncoverthe port 10 and. permit the excess uid to escape to the reservoir |2 byway of ports 10 and;v 28.

Although this invention has been described in connection with certainspecific embodiments,

the principles involved are susceptible of numerv ous other applicationsthat will readily occur to persons skilled in the art. The invention is.therefore, to be limited only by the scope of the appended claims.

Having thus described the various features of the invention, what Iclaim as new and desire to secure by Letters Patent is:`

l.- A fluid pressure producing device comprising a cylinder, a pistonreciprocable in the cylinder having a chamber therein provided with aport opening through the head of the piston, a plunger movable in thechamber having an extension adapted to enter and close the port, apiston movable on the extension, a spring for urging said piston todischarge fluid from said chamber and a pressure relief port controlledby said piston.

2. A fluid pressure producing device comprising a cylinder, a pistonreciprocable in the cylinder having a reduced body portion providing anannular chamber, a chamber in the piston provided with portscommunicating with the annular chamber and a port opening through thehead `of the piston, a plunger movable in the chamber having anextension adapted to enter and close the port opening through the headof the piston, a piston movable on the extension, a spring for urgingsaid piston to discharge fluid from said chamber, and a pressure relieflport controlled by said piston.

3. .A uid pressure producing devlce'comprising a reservoir, a cylindercommunicating therewith, a piston reciprocable in the cylinder having areduced body portion providing an annular chamber communicating with thereservoir and that portion of the cylinder forward of the piston, achamber in the piston onmunicating with the annular chamber and thatportion of the cylinder forward of the piston,l a plunger reciprocablein the chamber having a part adapted to close the communication betweenthe chamber and that portion of the cylinder forward of the piston, av

, portion providing an annular chamber communicating With the reservoir,the head 0f the piston having controlled 'ports providing communicationsbetween the annular chamber and that portion of the cylinder forward ofthe piston, a chamber in the piston communicating with the v annularchamber and with that portion of the cylinder forward of the piston, aplunger in the chamber having an extension adapted to close thecommunication between the chamber and that portion of the cylinderforward of the pis-r ton, a sealing cup seated on the head of theplunger, a piston resilientlysupported on the extension, and a sealingcup on the head of the piston on the extension, said sealing cupcontrolling communication between the piston chamber and the annularchamber. l

5. A iiuid pressure producing device comprising a reservoir, a cylindercommunicating therewith having a controlled discharge port, a pistonreciprocable in the cylinder having a reduced body portion providing anannular chamber communieating with the reservoir and spaced ports in itshead providing communications between the annular chamber and' thatportion of the cylinder forward of the piston, a sealing cup on the headof the piston controlling the ports therein, a chamber in the pistonhaving spaced ports communicating with the annular chamber and a portopening through the head of the piston, a plunger reciprocable in thechamber having an extension adapted to enter and close the port in thehead of the piston, a sealing cup on the plunger, a piston on theextension, a sealing cup carried by 'the piston on the extension,saidlast-named sealing cup controlling communication between the pistonchamber and the annular chamber, a spring interposed between the sealingcup on the Vplunger and the piston on the extension, and a v springinterposed between the cup carried by the -piston on the extension'andthe head of the chamber. HERBERT C. BOWEN,

